Automatic daylight X-ray film handling systems using cassettes have come into increased use in recent years. Typically such systems include apparatus for receiving an X-ray cassette containing an exposed X-ray film sheet, subsequently automatically opening the cassette, removing the exposed film sheet, placing an unexposed sheet in the cassette and closing the cassette.
U.S. Pat No. 3,150,263 describes such an apparatus, in which a plurality of predetermined size film sheet stacks are stored in individual magazines for loading into cassettes. In operation, a given X-ray cassette is inserted into a chamber which is then made light tight. The cassette is received onto a supporting rack and a system of microswitches determines the cassette size in terms of length and width. A control system, responding to the microswitch determination, opens the cassette lid, removes a film sheet from within the cassette for delivery to a storage means, selects an unexposed film sheet of a size commensurate with the cassette from the plurality of film sizes stored in the magazines, delivers the selected film sheet to the cassette, closes the cassette lid and ejects the loaded cassette. Similar apparatus is shown in U.K. published application No. 2,068,586A and U.S. Pat. No. 4,049,142.
In most such apparatus, the operator input is eliminated and microswitches or photodetectors, strategically placed in predetermined positions within the apparatus, detect the actual size of the cassette in order to determine the film size that must be dispensed to the cassette. Such apparatus is limited in its usefulness since it can only respond to the physical dimensions of the cassette, and is not able to detect and respond to film type or to perform other functions. In cases where (1) cassettes of similar dimensions but containing different types of intensifying screens must be loaded with different types of film, as contrasted to different size of film; (2) the inserted cassette may contain unexposed film to be first unloaded prior to loading with fresh film; (3) there is need to provide an additional exposure of patient identification information on the unloaded film as it exits the cassette, the prior art apparatus is unable to fulfill the need.
In other apparatus for automatically unloading and loading X-ray cassettes, the operator is required to input the information regarding film size and type. This is accomplished by a control panel on the outside of the apparatus. An operator may select a number of functions that the machine should perform for a particular cassette and film inserted. Unfortunately, such manual programming is prone to error. For example, if the operator inadvertently misprograms or malprograms, the result could be jamming of the machine, loading the wrong film type into the cassette or worse, damaging an exposed film by not removing it, or exposing a film with the wrong patient identification.